1. Field of the invention
The present invention relates to an electrophotographic apparatus, and more precisely it relates to a developing apparatus thereof.
2. Description of Related Art
In an electrophotographic apparatus, an electrostatic latent image is formed on an electrostatic photosensitive drum, such as a selenium drum which is uniformly charged, so that a toner or a color toner (including black), which is charged with electric charges having the same polarity as that of the electric charges with which the photosensitive drum is charged, is applied to the latent image to develop the toner. The developed toner is then transferred to an object, such as paper, by a transfer charging process. This kind of electrophotographic apparatus is widely used in image processing apparatus, such as a copier or a transfer type of facsimile.
There are two types of developers, one having a single component and the other having two components, i.e., a toner and a carrier which is mixed with the toner at a predetermined mixing ratio, used in the developing apparatus in of an the electrophotographic apparatus. The two-component developer has a higher resolving power than the one-component developer. When the two-component developer comes into contact with the photosensitive drum, the toner is applied to the latent image and the carrier is recovered. To achieve good development, it is necessary to bring the developer into uniform contact with the photosensitive drum in all directions of the photosensitive drum, including the axial direction thereof. Also, the toner must be uniformly mixed with the carrier. It should be remembered that the toner is consumed but the carrier is not. Accordingly, it is necessary to detect the consumption of the toner in order to supplementarily feed toner in accordance with the results of such detection, to thereby maintain the mixing ratio of the toner and the carrier within a predetermined range.
To this end, it is known to provide in a developing unit a stirrer (agitator) for stirring the toner, a supplemental feeder for supplementarily feeding the toner, and/or a toner sensor for detecting the consumption of the toner. However, the conventional developing units are complex in construction and expensive with respect to their manufacturing cost.